Interpretive Summary: Remote sensing is gaining interest as a tool to detect and quantify imported fire ant mounds. An experiment was conducted to examine seasonal differences in fire ant mound characteristics that might affect detection in airborne digital images. ARS researchers discovered that mounds exhibit predictable, seasonal changes in shape, becoming more elliptic (oval) during colder months. Seasonal changes in other mound characteristics that might influence detection, such as size and vegetation cover, were detected and described. These results will help researchers predict the time of year best suited for collection of remote sensing data for fire ant mound detection.

Technical Abstract:
Individual mound characteristics of Solenopsis richteri Forel, the black imported fire ant, were studied for one year in northern Mississippi pastures. Mounds were largest in May and smallest in November (41.5 ± 4.7 and 26.2 ± 4.1 L, respectively). Vegetation cover (vegetation growing from the mound surface) was greatest in August (75.8 ± 3.8 %) and lowest in November (34.1 ± 3.7 %); vegetation cover was about 30% greater on inactive (= abandoned) mounds than active mounds in February and May, but statistically similar in August and November. The proportion of mounds that were active ranged from 68 to 75%. Mounds were more eccentric during cooler months than during the summer. Seasonal changes in mound characteristics are discussed in light of their possible effects on mound detection using remote sensing techniques.